1) Field of Invention
The present invention concerns a method of control over sea navigation.
2) Description of Prior Act
Despite all detection and control methods available at the present time, the safety of sea traffic in high traffic density zones, particularly coastal and port zones, is not always guaranteed.
In order to guarantee safety, it is important to set up a secure communication system firstly between ships located in the same zone, and secondly between these ships and a maritime traffic control center monitoring this zone.
At the present time there are various methods of communication between vehicles and/or for pinpointing vehicles.
For land traffic, radiotelephone communications are used with coded destination addressing, but this type of system does not enable the user to pinpoint his correspondent.
More complexed equipment (such as GEOSTAR/LOCSTAR) can be used for communications and for pinpointing; a central station communicates with a mobile station through two circuits each passing through a satellite. The forward-return time necessary for exchanging communications can be used to determine distances from the mobile to the two satellites, and therefore to pinpoint it. This system combines addressing and pinpointing but uses only satellite communications and demands long range communication links.
For air traffic, secondary radar, particularly in S mode, can be used to communicate with an aircraft and simultaneously gives the position and identity. Like the GEOSTAR/LOCSTAR system, this radar combines addressing and pinpointing. Radar is badly adapted to the acquisition of addresses in a dense medium and requires complicated traffic management.
The ADS (Automatic Dependence Surveillance) concept was introduced more recently, and can determine the position and identity of an aircraft (which itself transmits the necessary information) and communicate with it. This system is efficient, but it does not enable participants to communicate between themselves without passing through the control center.
Concerning ships, the only communication method used worldwide at the present time is radiocommunication, generally in VHF, without addressing. Communications are set up on a predefined frequency, or channel, for each geographic area. These methods do not enable the user to correspond with a specific correspondent.
Satellite communications (such as INMARSAT) are starting to be used, and their coverage is almost worldwide due to the number and position of usable satellites. Links are set up by sending a destination address code.
French patents 2 601 168 and 2 661 536 use a system enabling ships to mutually locate each other, particularly in a dense environment (port zone, . . . ) and to safely and unambiguously communicate between themselves using addresses in order to prevent collisions. However, these systems do not enable a control center, for example a port control center, to start a communication with one or several specific ships, or with all ships located in its surveillance area.